Chapter 1

Introduction

Computer Networking:
A Top Down Approach ,
5th edition.
diti
Jim Kurose, Keith Ross
Addison-Wesley, April
2009.

Introduction

1-1

Chapter 1: Introduction
Our goal:

get feel and

tterminology
i l
more depth, detail
later in course
approach:
use Internet as
example

Overview:
whats the Internet?
whats a protocol?
network edge; hosts, access

net, physical media

network core: packet/circuit
switching, Internet structure
performance: loss,
loss delay
delay,
throughput
security
protocol layers, service models
history
Introduction

1-2

Chapter 1: roadmap
1.1 What is the Internet?
1 2 Network edge
1.2
end systems, access networks, links

1.3 Network core

circuit switching, packet switching, network structure

1.4 Delay, loss and throughput in packet-switched

networks
1 5 Protocol
1.5
P
l layers,
l
service
i models
d l
1.6 Networks under attack: security
1.7 History
Introduction

1-3

Whats the Internet: nuts and bolts view

millions of connected

PC

computing devices:

server

hosts = end systems

wireless
laptop
running network
cellular
handheld
apps
communication links
fiber, copper,
radio, satellite
transmission
rate = bandwidth
routers: forward
packets (chunks of
data)

access
points
wired
links

router

Mobile network
Global ISP

Home network
Regional ISP

Institutional network

Introduction

1-4

Cool internet appliances

Web-enabled toaster +
weather forecaster
IP picture frame
http://www.ceiva.com/

Worlds smallest web server

http://www-ccs.cs.umass.edu/~shri/iPic.html

Internet phones
Introduction

1-5

Whats the Internet: nuts and bolts view

protocols control sending,

receiving of msgs

Mobile network

e.g., TCP
TCP, IP
IP, HTTP,
HTTP Skype,
Sk
Ethernet

Internet: network of
networks

loosely hierarchical
public Internet versus
private intranet

Global ISP

Home network
Regional ISP

Institutional network

Internet standards
RFC: Request for comments
IETF: Internet Engineering
Task Force
Introduction

1-6

Whats the Internet: a service view

communication

infrastructure enables

distributed applications
applications:
Web, VoIP, email, games,
e-commerce, file sharing
communication services
provided to apps:
reliable data delivery
from source to
destination
best effort (unreliable)
data delivery
Introduction

1-7

Whats a protocol?
human protocols:
whats the time?
I have a question
introductions
specific msgs sent
specific actions taken
when msgs received,
received
or other events

network protocols:
machines rather than
h
humans
all communication
activity in Internet
governed by protocols

protocols define format,

order of msgs sent and
received among network
entities, and actions
taken on msg
transmission, receipt
Introduction

1-8

Whats a protocol?
a human protocol and a computer network protocol:
Hi

TCP connection
request

Hi

TCP connection
response

Got the
time?

Get http://www.awl.com/kurose-ross

2:00

<file>
time

Q: Other human protocols?

Introduction

1-9

Chapter 1: roadmap
1.1 What is the Internet?
1 2 Network edge
1.2
end systems, access networks, links

1.3 Network core

circuit switching, packet switching, network structure

1.4 Delay, loss and throughput in packet-switched

networks
1 5 Protocol
1.5
P
l layers,
l
service
i models
d l
1.6 Networks under attack: security
1.7 History
Introduction

1-10

A closer look at network structure:

network edge:

applications
pp
and
hosts
access networks,
physical media:
wired, wireless
communication links
network core:

interconnected
routers
network of
networks

Introduction

1-11

Introduction

1-12

The network edge:

end systems (hosts):

run application programs

e.g. Web, email
at edge of network

peer-peer

client/server model

client host requests, receives

service from always-on server
client/server
e.g. Web browser/server;
email
m il client/server
li nt/s

peer-peer model:

minimal (or no) use of

dedicated servers
e.g. Skype, BitTorrent

Access networks and physical media

Q: How to connect end
systems to edge router?
residential
d
l access nets
institutional access

networks (school,
company)
mobile access networks

Keep in mind:
bandwidth (bits per

second) of access
network?
shared or dedicated?
Introduction

1-13

Dial-up Modem
central
office

home
PC

home
dial-up
modem

telephone
network

Internet

ISP
modem
(e.g., AOL)

Uses existing telephony infrastructure

Home is connected to central office
up to 56Kbps direct access to router (often less)
Cant surf and phone at same time: not always on

Digital Subscriber Line (DSL)

Existing phone line:
0-4KHz phone; 4-50KHz
upstream data; 50KHz-1MHz
downstream data

home
phone

Internet

DSLAM

telephone
network

splitter
DSL
modem
home
PC

central
office

Also uses existing telephone infrastruture

up to 1 Mbps upstream (today typically < 256 kbps)
up to 8 Mbps downstream (today typically < 1 Mbps)
dedicated physical line to telephone central office

Residential access: cable modems

Does not use telephone infrastructure
Instead uses cable TV infrastructure
HFC: hybrid fiber coax

asymmetric: up to 30Mbps downstream, 2

Mbps upstream
network of cable and fiber attaches homes to
ISP router
homes share access to router
unlike DSL, which has dedicated access

Introduction

1-16

Residential access: cable modems

Diagram: http://www.cabledatacomnews.com/cmic/diagram.html

Introduction

1-17

Cable Network Architecture: Overview

Typically 500 to 5,000 homes

cable headend
cable distribution
network (simplified)

home

Introduction

1-18

Cable Network Architecture: Overview

server(s)

cable headend
cable distribution
network

home

Introduction

1-19

Introduction

1-20

Cable Network Architecture: Overview

cable headend
cable distribution
network (simplified)

home

10

Cable Network Architecture: Overview

FDM (more shortly):
V
I
D
E
O

V
I
D
E
O

V
I
D
E
O

V
I
D
E
O

V
I
D
E
O

V
I
D
E
O

D
A
T
A

D
A
T
A

C
O
N
T
R
O
L

Channels

cable headend
home

cable distribution
network

Introduction

1-21

Fiber to the Home

ONT
optical
fibers

Internet

OLT
central office

ONT

optical
fiber

optical
splitter
ONT

Optical
p
links from central office to the home
Two competing optical technologies:
Passive Optical network (PON)
Active Optical Network (PAN)
Much higher Internet rates; fiber also carries

television and phone services

11

Ethernet Internet access

100 Mbps

Institutional
router
Ethernet
switch

To Institutions
ISP

100 Mbps

1 Gbps
100 Mbps

server

Typically used in companies, universities, etc

10 Mbs, 100Mbps, 1Gbps, 10Gbps Ethernet
Today, end systems typically connect into Ethernet

switch

Wireless access networks

shared

wireless access

network connects end system

to router

via base station aka access

point

router
base

wireless LANs:
station
802.11b/g (WiFi): 11 or 54 Mbps
wider-area wireless access
provided by telco operator
~1Mbps over cellular system
(EVDO, HSDPA)
next up (?): WiMAX (10s Mbps)
over wide area

mobile
hosts
Introduction

1-24

12

Home networks
Typical home network components:
DSL or cable modem
router/firewall/NAT
t /fi
ll/NAT
Ethernet
wireless access
point
to/from
cable
headend

cable
l
modem

wireless
laptops

router/
firewall

wireless
access
point

Ethernet

Introduction

1-25

Physical Media
Bit: propagates between

transmitter/rcvr pairs
physical link: what lies
between transmitter &
receiver
guided media:

signals propagate in solid

media: copper,
copper fiber,
fiber coax

Twisted Pair (TP)

two insulated copper
wires

Category 3: traditional
phone wires, 10 Mbps
Ethernet
Category 5:
100Mbps Ethernet

unguided media:
signals propagate freely,
e.g., radio
Introduction

1-26

13

Physical Media: coax, fiber

Coaxial cable:

Fiber optic cable:

conductors
d t
bidirectional
baseband:

pulses, each pulse a bit

pulses
high-speed operation:

two concentric copper

single channel on cable

legacy Ethernet

broadband:
multiple channels on
cable
HFC

glass fiber carrying light

high-speed point-to-point
transmission (e.g., 10s100s Gps)

low error rate: repeaters

spaced far apart ; immune

to electromagnetic noise

Introduction

1-27

Physical media: radio

signal carried in

electromagnetic
spectrum
no physical wire
bidirectional
propagation
environment effects:

reflection
obstruction by objects
interference

Radio link types:

terrestrial microwave
e.g. up to
t 45 Mbps
Mb channels
h
l
LAN (e.g., Wifi)
11Mbps, 54 Mbps
wide-area (e.g., cellular)
3G cellular: ~ 1 Mbps
satellite
Kbps to 45Mbps channel (or
multiple smaller channels)
270 msec end-end delay
geosynchronous versus low
altitude
Introduction

1-28

14

Chapter 1: roadmap
1.1 What is the Internet?
1 2 Network edge
1.2
end systems, access networks, links

1.3 Network core

circuit switching, packet switching, network structure

1.4 Delay, loss and throughput in packet-switched

networks
1 5 Protocol
1.5
P
l layers,
l
service
i models
d l
1.6 Networks under attack: security
1.7 History
Introduction

1-29

Introduction

1-30

The Network Core

mesh of interconnected

routers
the fundamental
question: how is data
transferred through net?
circuit switching:
dedicated circuit per
call: telephone net
packet-switching: data
sent thru net in
discrete chunks

15

Network Core: Circuit Switching

End-end resources
reserved for call
call
link bandwidth, switch

capacity
dedicated resources:
no sharing
circuit-like
(guaranteed)
performance
call setup required

Introduction

1-31

Network Core: Circuit Switching

network resources
(e.g., bandwidth)
divided into pieces
pieces allocated to calls
resource piece

idle if

dividing link bandwidth

into pieces
frequency division
time division

not used by owning call

(no sharing)

Introduction

1-32

16

Circuit Switching: FDM and TDM

Example:
FDM

4 users
frequency
time

TDM

frequency
time

Introduction

1-33

Numerical example
How long does it take to send a file of

640,000
640
000 bits from host A to host B over a
circuit-switched network?
All links are 1.536 Mbps
Each link uses TDM with 24 slots/sec
500 msec to establish end-to-end circuit

Lets work it out!

Introduction

1-34

17

Network Core: Packet Switching

each end-end data stream
divided into packets
user A, B packets
k
share
h
network resources
each packet uses full link
bandwidth
resources used as needed
Bandwidth division into pieces
Dedicated allocation
Resource reservation

resource contention:
aggregate resource
d
demand
d can exceed
d
amount available
congestion: packets
queue, wait for link use
store and forward:
packets move one hop
p
p
at a time

Node receives complete

packet before forwarding

Introduction

1-35

Packet Switching: Statistical Multiplexing

100 Mb/s
Ethernet

A
B

statistical multiplexing

1.5 Mb/s
queue of packets
waiting for output
link

Sequence of A & B packets does not have fixed pattern,

bandwidth shared on demand statistical multiplexing.
TDM: each host gets same slot in revolving TDM frame.
Introduction

1-36

18

Packet-switching: store-and-forward
L
R

takes L/R seconds to

transmit (push out)

packet of L bits on to
link at R bps

store and forward:

entire packet must

arrive at router before
it can be transmitted
on next link
delay = 3L/R (assuming
zero propagation delay)

Example:
L = 7.5 Mbits
R = 1.5 Mbps
transmission delay = 15
sec

more on delay shortly

Introduction

1-37

Packet switching versus circuit switching

Packet switching allows more users to use network!
1 Mb/s link
each user:
100 kb/s when active
active 10% of time

circuit-switching:

10 users

N users
1 Mbps link

packet switching:

with 35 users,
probability > 10 active
at same time is less
than .0004

Q: how did we get value 0.0004?

Introduction

1-38

19

Packet switching versus circuit switching

Is packet switching a slam dunk winner?
great for bursty data

resource sharing
simpler, no call setup
excessive congestion: packet delay and loss
protocols needed for reliable data transfer,
congestion control
Q: How to provide circuit-like behavior?
bandwidth guarantees needed for audio/video apps
still an unsolved problem (chapter 7)

Q: human analogies of reserved resources (circuit

switching) versus on-demand allocation (packet-switching)?

Introduction

1-39

Internet structure: network of networks

roughly hierarchical
at center: tier-1 ISPs (e.g.,
g Verizon, Sprint,
p
AT&T,

Cable and Wireless), national/international coverage

treat each other as equals
Tier-1
providers
interconnect
(peer)
privately

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

Introduction

1-40

20

Tier-1 ISP: e.g., Sprint

POP: point-of-presence

to/from backbone
peering

to/from customers

Introduction

1-41

Internet structure: network of networks

Tier-2 ISPs: smaller (often regional) ISPs
Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs

Tier-2 ISP pays

tier-1 ISP for
connectivity to
rest of Internet
tier-2 ISP is
customer of
tier-1 provider

Tier-2 ISP

Tier-2 ISP

Tier 1 ISP

Tier 1 ISP
Tier-2 ISP

Tier 1 ISP

Tier-2 ISPs
also peer
privately with
each other.

Tier-2 ISP

Tier-2 ISP
Introduction

1-42

21

Internet structure: network of networks

Tier-3 ISPs and local ISPs
last hop (access) network (closest to end systems)
local
ISP
Local and tier3 ISPs are
customers of
higher tier
ISPs
connecting
them to rest
of Internet

Tier 3
ISP
Tier-2 ISP

local
ISP

local
ISP

local
ISP
Tier-2 ISP

Tier 1 ISP
Tier 1 ISP

Tier 1 ISP

Tier-2 ISP
local
local
ISP
ISP

Tier-2 ISP
local
ISP

Tier-2 ISP
local
ISP
Introduction

1-43

Internet structure: network of networks

a packet passes through many networks!

local
ISP

Tier 3
ISP
Tier-2 ISP

local
ISP

local
ISP

local
ISP
Tier-2 ISP

Tier 1 ISP

Tier 1 ISP
Tier-2 ISP
local
local
ISP
ISP

Tier 1 ISP
Tier-2 ISP
local
ISP

Tier-2 ISP
local
ISP
Introduction

1-44

22

Chapter 1: roadmap
1.1 What is the Internet?
1 2 Network edge
1.2
end systems, access networks, links

1.3 Network core

circuit switching, packet switching, network structure

1.4 Delay, loss and throughput in packet-switched

networks
1 5 Protocol
1.5
P
l layers,
l
service
i models
d l
1.6 Networks under attack: security
1.7 History
Introduction

1-45

How do loss and delay occur?

packets queue in router buffers
p
packet arrival rate to link exceeds output
p link

capacity
packets queue, wait for turn

packet being transmitted (delay)

A
B

packets queueing (delay)

free (available) buffers: arriving packets
dropped (loss) if no free buffers

Introduction

1-46

23

Four sources of packet delay

1. nodal processing:
check bit errors
determine output link

2. queueing
time waiting at output
link for transmission
depends on congestion
level of router

transmission

propagation

nodal
processing

queueing
Introduction

1-47

Delay in packet-switched networks

3. Transmission delay:
R=link bandwidth (bps)
L=packet length (bits)
time to send bits into
link = L/R

t
transmission
smissi

4. Propagation delay:
d = length of physical link
s = propagation speed in
medium (~2x108 m/sec)
propagation delay = d/s
Note: s and R are very
different quantities!

propagation

nodal
processing

queueing

Introduction

1-48

24

Caravan analogy
100 km
ten-car
caravan

100 km

toll
booth

toll
booth

cars propagate at

100 km/hr
toll booth takes 12 sec to
service car (transmission
time))
car~bit; caravan ~ packet
Q: How long until caravan
is lined up before 2nd toll
booth?

Time to push entire

caravan through toll

booth onto highway =
12*10 = 120 sec
Time for last car to
propagate from 1st to
2nd toll both:
100km/(100km/hr)= 1 hr
A: 62 minutes
Introduction

1-49

Caravan analogy (more)

100 km
ten-car
caravan

100 km

toll
booth

Cars now propagate at

1000 km/hr
Toll booth now takes 1
min to service a car
Q: Will cars arrive to
2nd booth before all
cars serviced at 1st
booth?

toll
booth

Yes! After 7 min, 1st car

at 2nd booth and 3 cars

still at 1st booth.
1st bit of packet can
arrive at 2nd router
before packet is fully
transmitted at 1st router!

See Ethernet applet at AWL

Web site
Introduction

1-50

25

Nodal delay
d nodal d proc d queue d trans d prop
dproc = processing delay
typically a few microsecs or less
dqueue = queuing delay
depends on congestion
dtrans = transmission delay
y
= L/R, significant for low-speed links
dprop = propagation delay
a few microsecs to hundreds of msecs

Introduction

1-51

Introduction

1-52

Queueing delay (revisited)

R=link bandwidth (bps)
L=packet length (bits)
a=average packet

arrival rate

traffic intensity = La/R

La/R
L /R ~ 0:
0 average queueing
i delay
d l small
ll
La/R -> 1: delays become large
La/R > 1: more work arriving than can be

serviced, average delay infinite!

26

Real Internet delays and routes

What do real Internet delay & loss look like?
Traceroute program: provides delay

measurement from source to router along end-end

Internet path towards destination. For all i:

sends three packets that will reach router i on path

towards destination
router i will return packets to sender
sender times interval between transmission and reply.
py
3 probes

3 probes

3 probes
Introduction

1-53

Real Internet delays and routes

traceroute: gaia.cs.umass.edu to www.eurecom.fr
Three delay measurements from
gaia.cs.umass.edu
g
m
to cs-gw.cs.umass.edu
g
m
1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms
2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms
3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms
4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms
5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms
6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms
7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms trans-oceanic
8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms
link
9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms
10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms
11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms
12 nio-n2.cssi.renater.fr
nio n2 cssi renater fr (193
(193.51.206.13)
51 206 13) 111 ms 114 ms 116 ms
13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms
14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms
15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms
16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms
17 * * *
* means no response (probe lost, router not replying)
18 * * *
19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms
Introduction

1-54

27

Packet loss
queue (aka buffer) preceding link in buffer has

finite capacity
packet arriving to full queue dropped (aka lost)
lost packet may be retransmitted by previous
node, by source end system, or not at all
buffer
((waiting
g area))

A
B

packet being transmitted

packet arriving to
full buffer is lost
Introduction

1-55

Throughput
throughput: rate (bits/time unit) at which

bits transferred between sender/receiver

instantaneous: rate at given point in time
average: rate over longer period of time

link
capacity
that
can carry
server,
with
server
sends
bits pipe
R
bits/sec
fluid
at
rate
file
of
F
bits
s
(fluid) into pipe
Rs bits/sec)
to send to client

link that
capacity
pipe
can carry
Rfluid
c bits/sec
at rate
Rc bits/sec)
Introduction

1-56

28

Throughput (more)
Rs

< Rc What is average end-end throughput?

Rs bits/sec

Rs

Rc bits/sec

> Rc What is average end-end throughput?

Rs bits/sec
bits/s

Rc bits/sec
bit /

bottleneck link
link on end-end path that constrains end-end throughput
Introduction

1-57

Throughput: Internet scenario

per-connection

end-end
throughput:
min(Rc,Rs,R/10)
in practice: Rc or
Rs is
i often
ft
bottleneck

Rs
Rs

Rs
R

Rc

Rc
Rc

10 connections (fairly) share

backbone bottleneck link R bits/sec
Introduction

1-58

29

Chapter 1: roadmap
1.1 What is the Internet?
1 2 Network edge
1.2
end systems, access networks, links

1.3 Network core

circuit switching, packet switching, network structure

1.4 Delay, loss and throughput in packet-switched

networks
15P
1.5
Protocoll layers,
l
service
i models
d l
1.6 Networks under attack: security
1.7 History
Introduction

1-59

Protocol Layers
Networks are complex!
many pieces:
hosts
routers
links of various
media
applications
protocols
hardware,
software

Question:
Is there any hope of
organizing structure of
network?
Or at least our discussion
of networks?

Introduction

1-60

30

Organization of air travel

ticket (purchase)

ticket (complain)

baggage (check)

baggage (claim)
l

gates (load)

gates (unload)

runway takeoff

runway landing

airplane routing

airplane routing
airplane
l
routing

a series of steps
Introduction

1-61

Layering of airline functionality

ticket (purchase)

ticket (complain)

ticket

baggage (check)

baggage (claim

baggage

gates (load)

gates (unload)

gate

runway (takeoff)

runway (land)

takeoff/landing

airplane routing

airplane routing

airplane routing
departure
airport

airplane routing

airplane routing

intermediate air-traffic
control centers

arrival
airport

Layers: each
L
h layer
l
implements
i l
t a service
i
via its own internal-layer actions
relying on services provided by layer below
Introduction

1-62

31

Why layering?
Dealing with complex systems:
explicit structure allows identification,

relationship of complex systems pieces

layered reference model for discussion
modularization eases maintenance, updating of
system
change of implementation of layers service
transparent to rest of system
e.g., change in gate procedure doesnt affect
rest of system
layering considered harmful?
Introduction

1-63

Internet protocol stack

application: supporting network

applications

FTP, SMTP, HTTP

transport: process-process data

transfer

TCP, UDP

network: routing of datagrams from

source to destination

IP, routing protocols

link: data transfer between

application
pp
transport
network
link
physical

neighboring network elements

PPP, Ethernet

physical: bits on the wire

Introduction

1-64

32

ISO/OSI reference model

presentation: allow applications to

interpret meaning of data, e.g.,

encryption,
ti
compression,
i
machinehi
specific conventions
session: synchronization,
checkpointing, recovery of data
exchange
Internet stack missing these
layers!
these services, if needed, must
be implemented in application
needed?

application
presentation
session
transport
network
link
physical

Introduction

Encapsulation

source
message
segment

Ht

datagram Hn Ht

frame Hl Hn Ht

1-65

application
transport
network
link
physical

link
physical
switch

destination
M
Ht

Hn Ht

Hl Hn Ht

application
transport
network
link
physical

Hn Ht

Hl Hn Ht

network
link
physical

Hn Ht

router

Introduction

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33

Chapter 1: roadmap
1.1 What is the Internet?
1 2 Network edge
1.2
end systems, access networks, links

1.3 Network core

circuit switching, packet switching, network structure

1.4 Delay, loss and throughput in packet-switched

networks
1 5 Protocol
1.5
P
l layers,
l
service
i models
d l
1.6 Networks under attack: security
1.7 History
Introduction

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Network Security
The field of network security is about:
how bad guys
y can attack computer
p
networks
how we can defend networks against attacks
how to design architectures that are immune to
attacks
Internet not originally designed with

(much) security in mind

original vision: a group of mutually trusting

users attached to a transparent network

Internet protocol designers playing catch-up
Security considerations in all layers!
Introduction

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34

Bad guys can put malware into

hosts via Internet
Malware can get in host from a virus, worm, or

trojan horse.

Spyware malware can record keystrokes, web

sites visited, upload info to collection site.

Infected host can be enrolled in a botnet, used

for spam
p
and DDoS attacks.

Malware is often self-replicating: from an

infected host, seeks entry into other hosts

Introduction

1-69

Bad guys can put malware into

hosts via Internet
Trojan horse
Hidden part of some
otherwise useful
software
Today often on a Web
page (Active-X, plugin)
Virus
infection by receiving
object (e.g.,
(e g e
e-mail
mail
attachment), actively
executing
self-replicating:
propagate itself to
other hosts, users

Worm:
infection by
y passively
p
y
receiving object that gets
itself executed
self- replicating: propagates
to other hosts, users
Sapphire Worm: aggregate scans/sec
in first 5 minutes of outbreak (CAIDA, UWisc data)

Introduction

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35

Bad guys can attack servers and

network infrastructure
Denial of service (DoS): attackers make resources

g
traffic
(server, bandwidth) unavailable to legitimate
by overwhelming resource with bogus traffic

1.

select target

2. break into hosts

around the network

(see botnet)
3. send
d packets
k t ttoward
d
target from
compromised hosts

target

Introduction

1-71

The bad guys can sniff packets

Packet sniffing:
broadcast media (shared Ethernet, wireless)
promiscuous network interface reads/records all
packets (e.g., including passwords!) passing by

src:B dest:A

payload

Wireshark software used for end-of-chapter

labs is a (free) packet-sniffer
Introduction

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36

The bad guys can use false source

addresses
IP

spoofing: send packet with false source address

C

A
src:B dest:A

payload

Introduction

1-73

The bad guys can record and

playback
record-and-playback: sniff sensitive info (e.g.,
password),
d) and
d use llater
t
password holder is that user from system point of
view

src:B dest:A

user: B; password: foo

B
Introduction

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37

Network Security
more throughout this course
chapter
p
8: focus
f
on security
y
crypographic techniques: obvious uses and

not so obvious uses

Introduction

1-75

Chapter 1: roadmap
1.1 What is the Internet?
1 2 Network edge
1.2
end systems, access networks, links

1.3 Network core

circuit switching, packet switching, network structure

1.4 Delay, loss and throughput in packet-switched

networks
1 5 Protocol
1.5
P
l layers,
l
service
i models
d l
1.6 Networks under attack: security
1.7 History
Introduction

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38

Internet History
1961-1972: Early packet-switching principles
1961: Kleinrock - queueing

theory shows
effectiveness of packetswitching
1964: Baran - packetswitching in military nets
1967: ARPAnet conceived
by Advanced Research
Projects Agency
1969: first ARPAnet node
operational

1972:

ARPAnett public
ARPA
bli demonstration
d
t ti
NCP (Network Control Protocol)
first host-host protocol
first e-mail program
ARPAnet has 15 nodes

Introduction

1-77

Internet History
1972-1980: Internetworking, new and proprietary nets
1970: ALOHAnet satellite

network in Hawaii
1974: Cerf and Kahn architecture for
interconnecting networks
1976: Ethernet at Xerox
PARC
ate70s: proprietary
architectures: DECnet, SNA,
XNA
late 70s: switching fixed
length packets (ATM
precursor)
1979: ARPAnet has 200 nodes

Cerf and Kahns internetworking

principles:
pr
nc ples
minimalism, autonomy - no
internal changes required
to interconnect networks
best effort service model
stateless routers
decentralized control
define todays Internet
architecture

Introduction

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39

Internet History
1980-1990: new protocols, a proliferation of networks
1983: deployment of

TCP/IP
1982: smtp e-mail
protocol defined
1983: DNS defined
for name-to-IPaddress translation
1985: ftp protocol
defined
1988: TCP congestion
control

new national networks:

Csnet, BITnet,
C
BIT
NSFnet, Minitel
100,000 hosts
connected to
confederation of
networks

Introduction

1-79

Internet History
1990, 2000s: commercialization, the Web, new apps
Early 1990s: ARPAnet

decommissioned
1991: NSF lifts restrictions on
commercial use of NSFnet
(decommissioned, 1995)
early 1990s: Web
hypertext [Bush 1945, Nelson
1960s]
HTML,
HTML HTTP:
HTTP B
Berners-Lee
L
1994: Mosaic, later Netscape
late 1990s:
commercialization of the Web

Late 1990s 2000s:

more killer apps: instant

messaging, P2P file sharing

network security to

forefront
est. 50 million host, 100
million+ users
backbone links running
g at
Gbps

Introduction

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40

Internet History
2007:
~500 million hosts
Voice, Video over IP
P2P applications: BitTorrent
(file sharing) Skype (VoIP),
PPLive (video)
more applications: YouTube,
gaming
wireless, mobility

Introduction

1-81

Introduction: Summary
Covered a ton of material!
Internet overview
whats
h a protocol?
l?
network edge, core, access
network
packet-switching versus
circuit-switching
Internet structure
performance:
f
lloss, delay,
d l
throughput
layering, service models
security
history

You now have:

context, o
overview,
er ew,
feel of networking
more depth, detail to

follow!

Introduction

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41